Renal Lecture 1 Flashcards
How do kidneys impact every body function?
through regulation of body fluids
What are the 3 things the kidneys excrete?
- water
- electrolytes (Na, K, Cl, HCO3, H, Ca, Pi)
- waste products
What are the 4 things the kidneys regulate?
- body fluid volume
- body fluid composition
- body fluid osmolarity
- body fluid pH
Give an example for why it’s important that urine output is regulated
on a hot day you sweat more, if urine output remained the same, intake and output of water would no longer match and we would become seriously dehydrated
therefore, kidneys must be able to alter how much urine is being excreted to match other methods of water loss that are not regulated internally
- important in keeping both the volume and composition of body fluids constant
Osmolarity vs osmolality
osmolarity: moles of solute per litre of solvent
*temperature dependent
osmolality: moles of solvent per kilogram of solvent
*temperature independent
Osmotic pressure
driving force for water movement (pressure)
dependent on:
- solute concentration
- ability to permeate the membrane (reflection coefficient => 0-1)
Fluid composition vs fluid osmolarity/ osmotic pressure throughout body
composition: very different
osmolarity/ osmotic pressure: very similar
- if it was different, water would flow until gradient went away
Osmotic water flow across a cell membrane
water moves in response to an osmotic pressure difference (from low osmotic pressure, to high osmotic pressure)
- more stuff = more attractive
Isotonic solution vs hypertonic solution vs hypotonic solution
isotonic: same osmotic pressure, cell stays the same
hypertonic: high osmotic pressure, cell shrinks (water leaves cell, low => high)
hypotonic: low osmotic pressure, cell swells
What are the structures/ fluids coming in and out of the kidney?
IN:
blood (artery)
OUT:
blood (vein)
urine (ureter)
The kidneys produce ______ from ______
urine; blood
What are the 2 “layers” of the kidney? Where does the nephron start?
cortex (outer)
medulla (inner)
nephron starts at the cortex
The nephron (draw the structure too)
Bowman’s capsule contacts the glomerular capillary => leads to the proximal tubule => loop of henle => distal tubule => fluid leaves through collecting duct
Flow of urine: starts in cortex, goes down to medulla, goes back up to cortex, ends in medulla where it exits through the collecting duct
Macula densa: a portion of the distal tubule that comes in close contact with the glomerular capillary
How is urine formed? How is its composition changed after?
by filtration of blood by the glomerulus
composition is altered by processes of absorption and secretion as it passes through the nephron tubule (whats excreted is very different than whats formed through filtration)
Excreted fluid = ?
filtered - reabsorbed + secreted
What is the flow of fluid in filtration, reabsorption, secretion, and excretion?
- filtration (blood => urine)
- reabsorption (urine => blood)
secretion (blood => urine) - excretion (urine => bladder)
What is the filtration fraction?
GFR/RPF roughly 0.2
RPF = renal plasma flow
Where does glomerular filtration occur?
in Bowman’s capsule => made up of the afferent arteriole, efferent arteriole, macula densa, beginning of the proximal tubule and podocytes
What are podocytes
modified epithelial cells that form part of the filtration barrier
The filtrate (blood) passes through the glomerular barrier to form urine. What 3 layers make up this barrier?
- fenestrations
- basement membrane
- slit pores between podocytes
Explain the effect of size and charge of a substance on glomerular filtration
small > large
positive > negative
large substances (e.g., proteins) are not filtered, and remain in the blood
Filtration occurs because of what?
glomerular capillary starling forces
GFR = Kf x Pnet
Pnet is comprised of 4 pressures: 2 that favour filtration and 2 that oppose filtration
*must be positive for fluids to flow in from capillaries
What happens to the pressures as blood flows from afferent to efferent?
Pgc decreases slightly (fluid removed)
colloid osmotic pressure in the glomerular capillary increases slightly
leads to lower overall Pnet (Puf) at efferent end compared to afferent end
What are the effects of changing arteriolar resistance on Pgc, GFR and RBF?
- constrict afferent: decrease all 3
- constrict efferent: increase Pgc and GFR, decrease RBF
- dilate afferent: increase all 3
- dilate efferent: decrease Pgc and GFR, increase RBF
How does changing the GFR change urine excretion?
decreased GFR = decreased urine excretion (producing less urine)
increased GFR = increased urine excretion (producing more urine)
Vasoconstrictors vs vasodilators => influence on GFR and RBF
vasoconstrictors: all decrease GFR and RBF
vasodilators: mostly increase GFR and RBF
What are the 2 mechanisms of autoregulation of GFR and RBF? (Pgc is important in regulating GFR, why don’t we excrete more urine when our BP increases?)
- myogenic mechanism
- tubulogenic feedback
Myogenic mechanism of autoregulation
we expect an increase in pressure to increase both RBF and GFR
BUT
increased pressure => smooth muscle stretch => smooth muscle cell contraction => increased afferent arteriole resistance => decreased RBF and GFR
Tubulogenic feedback mechanism of autoregulation
increased pressure => increased NaCl sensed by macula densa => signal to JGA => increased afferent arteriole resistance => decreased RBF and GFR
Renal clearance
a measure of how readily a substance is removed by the kidneys
GFR/ clearance = [U] x F/ [P]
Inulin clearance (NOT insulin)
measure of GFR; inulin is not reabsorbed or secreted
- by measuring [inulin] in urine and plasma, and the rate of urine flow, we can calculate GFR
Creatine clearance
better than inulin clearance because it is in our bodies
creatine clearance = Ucr x V/ Pcr
creatine clearance is roughly equal to GFR
no/little reabsorption and secretion
What is a simple clinical measure of GFR?
plasma [creatine] because it is mainly excreted through urine
- an indication of how well the kidneys are filtering
- low GFR = build up of creatine => can measure this in blood
